The present invention relates to the construction of systems for processing signals by means of elastic waves invariant with the temperature.
Elastic wave devices are used for numerous applications such for example as: for dispersive delay lines; for pulse compression; for filters; for spectrum analysers using several ".pi." or "T" structured dispersive lines and for correlators or convolvers.
For these applications, it is important that any frequency determined by reference to the elastic wave processing device is stable and, more especially, as dependent as little as possible on the temperature. In the opposite case, there is distortion of the output signal with respect to the expected output signal, which is all the greater the larger the temperature variations. This is the case when the equipment using elastic wave processing devices is subjected to large temperature variations, this is the case for example in the field of radar or sonar applications where the equipment is vehicle-borne.
So as to limit the effects due to temperature variations on the elastic wave components, it is known to use substrates and cuts for which the linear variations and the speed variations cancel out in the first order such as, for example, quartz cut according to an "ST" cut. However, these substrates present low coupling coefficients and substrates are generally used whose coupling coefficients are high such as Lithium Niobate (LiNbO.sub.3), Bismuth and Germanium Oxide (Bi.sub.12 GeO.sub.2) or Lithium Tantalate (LiTaO.sub.3). For these substrates, it is known to overcome the effects due to temperature variations by placing the device in a thermostatic enclosure for regulating the temperature of the substrate. However, these enclosures are consumers of energy and have a thermal inertia when brought into operation. This is a disadvantage for unforeseeable uses of short duration for which the temperature will not be stabilized.
To remedy these disadvantages, the signal processing system of the invention provides great operational stability over a wide temperature range, without a thermostatic enclosure by using clocks, slaved to the temperature, which control the different elements of the signal processing, allowing more especially contraction or expansion of the time of the signal, by means of two write and read memories.